A communication system can be seen as a facility that enables communication sessions between two or more entities such as mobile communication devices and/or other stations associated with the communication system. A communication system and a compatible communication device typically operate in accordance with a given standard or specification which sets out what the various entities associated with the system are permitted to do and how that should be achieved. For example, the manner how the communication device can access the communication system and how communications shall be implemented between communicating devices, the elements of the communication network and/or other communication devices is typically defined.
In a wireless communication system at least a part of communications between at least two devices occurs over a wireless link. Examples of wireless systems include public land mobile networks (PLMN), satellite based communication systems and different wireless local networks, for example wireless local area networks (WLAN). In wireless systems an access node is provided by a base station. The radio coverage area of a base station is known as a cell, and therefore the wireless systems are often referred to as cellular systems. They can also be called mobile communication systems or mobile communication networks.
A mobile telecommunication network typically operates in accordance with a wireless standard. Examples include GSM (Global System for Mobile) EDGE (Enhanced Data for GSM Evolution) Radio Access Networks (GERAN), Universal Terrestrial Radio Access Networks (UTRAN), and evolved Universal Terrestrial Radio Access Networks (EUTRAN).
A further example of wireless communication systems is an architecture that is being standardized by the 3rd Generation Partnership Project (3GPP). This system is often referred to as the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology. The aim of LTE is to achieve, inter alia, reduced latency, higher user data rates, improved system capacity and coverage, and reduced cost for the operator. A further development of the LTE is often referred to as LTE-Advanced.
In system according to the LTE standard a base station access node is called enhanced or evolved Node B.
A user can access the communication system by means of an appropriate communication device. A communication device of a user is often referred to as user equipment (UE) or terminal or mobile device or a mobile station. A communication device is provided with an appropriate signal receiving and transmitting arrangement for enabling communications with other parties. The device may also comprise user interface for communicating with the user and a controller for controlling the operation of the device.
A communication device may be arranged to communicate, for example, data for carrying communications such as voice, electronic mail (email), text message, multimedia, for enabling internet access, for carrying application specific data and so on. Users may thus be offered and provided numerous services via their communication devices. The communication connection can be provided by means of one or more data bearers.
In wireless systems a communication device provides a transceiver device that can communicate with another communication device such as e.g. an access node or a base station and/or another user equipment. The communication device may access a carrier provided by a base station and transmit and/or receive communications on the carrier.
A feature of wireless communication devices is that they offer mobility for the users thereof. A mobile communication device, or mobile device or mobile station for short, may also be transferred, or handed over, from a base station to another and even between base stations belonging to different systems.
A communication device or user equipment that has no continuous connection to its home system may nevertheless be considered as being a part of a communication system. In certain applications, for example in ad-hoc networks or in PSN i.e. public safety networks, the communication system may be based on use of a plurality of user equipment capable of communicating with each other. In this kind of situation the devices do not necessarily have a continuous connection to the own (PSN) network.
PSN networks are separate mobile communication networks that are used by law enforcement, rescue services, fire brigades and other public authorities or even public utilities for time and mission critical communication. In PSN networks the mobile devices may communicate directly with each other in Device to Device mode or in so called direct mode. The operation of PSN network must be fast, reliable and secure, regardless of lack of network coverage, lack of resources or any type of network failure. The PSN Network must have high availability, with no single point of failure, a highly resilient architecture and guaranteed availability even in times of a major incident, when the network will be stressed. It must also continue to operate through power outages.
The above requirements are difficult to fulfill, particularly with scarce resources. Also, sometimes on certain areas of the PSN network, resources are used only sporadically and therefore the usage intensity on that area is low. Therefore, it is sometimes not possible to build costly PSN networks to all areas, e.g. to all very sparsely populated or very remote areas, where the usage intensity is low.
This invention considers the problem how an available commercial cellular network may provide assistance in ensuring robustness of PSN mission critical operations and services in e.g. the following situations: 1) a base station site of PSN went off—out of service—e.g. as being destroyed in accident or disaster; 2) unexpected PSN failure that blocks the use of whole PSN; 3) a major incident happens in an area without PSN coverage—therefore network services are needed on this out of PSN coverage area; 4) an extremely large incident happens in an area of PSN—this leads to congestion of whole PSN—some other means of communication is needed for the devices thus being isolated from the PSN.
In particular this invention is related to a situation where at least two communication devices belonging to a PSN network lose their connections to their own PSN network but would still need the resources and connectivity of the PSN networks. Those communication devices would like to communicate to the PSN network, to other networks and devices in them or alternatively with each other. The problem that appears in this situation is how to effectively establish network connection and connectivity to these at least two communication devices without any undue delay. It is also possible that the at least two communication devices may attempt to simultaneously act as the device that controls the communication. This would consume more resources and delay the establishment of connections between the devices and other parts or services of the PSN network.